The present invention relates to a honeycomb structure suitably used as a catalyst carrier in a catalyst body for purifying an exhaust gas emitted from an internal combustion engine such as gasoline engine or the like, as well as to a catalytic converter comprising a honeycomb catalyst body and a housing holding the honeycomb catalyst body.
The exhaust gas emitted from an internal combustion engine such as gasoline engine or the like contains a large amount of harmful components such as nitrogen oxide (NOx), hydrocarbons, carbon monoxide and the like. These harmful components, when per se released into the air, cause environmental pollution; therefore, there is generally mounted, in an exhaust gas passage extending from the internal combustion engine, a catalyst body for purifying the harmful components contained in the exhaust gas.
As the catalyst body used for such a purpose, there can be mentioned, for example, a honeycomb catalyst body comprising                a honeycomb structure 1 as a catalyst carrier, such as shown in FIG. 1, in which a large number of cells 3 each functioning as a gas passage are formed by being surrounded by partition walls 4, and        an exhaust gas purification catalyst (e.g. a three-way catalyst) carried on the partition walls of the honeycomb structure.With such a honeycomb catalyst body, the purification of the harmful components contained in an exhaust gas is promoted, whereby the harmful components contained in the exhaust gas can be reduced and the exhaust gas can be purified effectively.        
Generally, the above honeycomb catalyst body is used in the form of, for example, a catalytic converter 11 such as shown in FIG. 2, comprising                a honeycomb catalyst body 12,        a housing which is cylindrical, can hold the honeycomb catalyst body 12, and has an exhaust gas-incoming section 13a at one end and a purified gas-outgoing section 13b at the other end, and        a holding material 14 interposed between the outer surface of the honeycomb catalyst body 12 and the inner surface of the housing 13,and is mounted in an exhaust gas passage extending from an internal combustion engine or the like [reference is made to, for example, Patent Literature 1 (U.S. Pat. No. 3,390,698)].        
In mounting the above catalytic converter in an exhaust gas passage, it is necessary to minimize the reduction in engine output caused by exhaust gas interference. The reason is that in a multi-cylinder (e.g. four cylinder or six cylinder) engine, when the exhaust gases emitted from the individual cylinders are combined in one passage, there is a difference in timings of exhaust gas discharge from various cylinders (i.e. timings of fuel combustion in the cylinders) and accordingly the high-pressure exhaust gas emitted from one cylinder prevents smooth exhaust gas discharge from other cylinder (this phenomenon is called exhaust gas interference), resulting in a reduction in engine output.
Hence, there has been adopted a structure such as shown in FIG. 3, wherein, first, exhaust pipes 22a and 22c (or 22b and 22d) alone of a multi-cylinder engine 21, extending from cylinders whose combustion orders are not continuous, are combined in one catalytic converter 23a (or 23b), finally, pipes extending from these two catalytic converters 23a and 23b are combined in one passage, and thus the catalytic converter 23a and the catalytic converter 23b are mounted in an exhaust gas passage 24 [reference is made to, for example, Patent Literature 2 (JP-A-2003-138962)].
Such a structure is very effective from a standpoint of preventing the reduction in engine output caused by exhaust gas interference; however, this structure requires at least two sets of honeycomb structures as a catalyst carrier, housings (e.g. metal cases) and holding materials (e.g. ceramic mats), making it difficult to use a catalytic converter of compact structure and, when the engine space is small, there has been a case in which mounting of catalytic converter is impossible. Further, the increase in the number of required parts has invited a complicated exhaust gas structure, an increased weight of vehicle body and an increased cost.